Objective determination of acoustic prescriptions

ABSTRACT

Presented herein are techniques that make use of objective measurements obtained in response to acoustic stimulation signals. More specifically, at least one measure of outer hair cell function and at least one measure of auditory nerve function are obtained from a tonotopic region of an inner ear of a recipient of a hearing prosthesis. The at least one measure of auditory nerve function and the least one measure of outer hair cell function are then analyzed relative to one another.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/801,885, filed Feb. 26, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/299,707, filed Oct. 21, 2016, the entirecontents of which is incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates generally to electro-acoustic hearingprostheses.

Related Art

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and/or sensorineural. Conductive hearing lossoccurs when the normal mechanical pathways of the outer and/or middleear are impeded, for example, by damage to the ossicular chain or earcanal. Sensorineural hearing loss occurs when there is damage to theinner ear, or to the nerve pathways from the inner ear to the brain.

Individuals who suffer from conductive hearing loss typically have someform of residual hearing because the hair cells in the cochlea areundamaged. As such, individuals suffering from conductive hearing losstypically receive an auditory prosthesis that generates motion of thecochlea fluid. Such auditory prostheses include, for example, acoustichearing aids, bone conduction devices, and direct acoustic stimulators.

In many people who are profoundly deaf, however, the reason for theirdeafness is sensorineural hearing loss. Those suffering from some formsof sensorineural hearing loss are unable to derive suitable benefit fromauditory prostheses that generate mechanical motion of the cochleafluid. Such individuals can benefit from implantable auditory prosthesesthat stimulate nerve cells of the recipient's auditory system in otherways (e.g., electrical, optical and the like). Cochlear implants areoften proposed when the sensorineural hearing loss is due to the absenceor destruction of the cochlea hair cells, which transduce acousticsignals into nerve impulses. An auditory brainstem stimulator is anothertype of stimulating auditory prosthesis that might also be proposed whena recipient experiences sensorineural hearing loss due to damage to theauditory nerve.

Certain individuals suffer from only partial sensorineural hearing lossand, as such, retain at least some residual hearing. These individualsmay be candidates for electro-acoustic hearing prostheses.

SUMMARY

In one aspect, a method is provided. The method comprises: obtaining aplurality of acoustically-evoked inner ear responses from an inner earof a recipient of an electro-acoustic hearing prosthesis; determining,based on the plurality of acoustically-evoked inner ear responses, oneor more input/output functions for at least one region of the inner ear;and determining, based on the one or more input/output functions, one ormore gain functions for use by the electro-acoustic hearing prosthesisin conversion of sound signals to acoustic stimulation signals fordelivery to the recipient.

In another aspect, an electro-acoustic hearing prosthesis system isprovided. The electro-acoustic hearing prosthesis system comprises: anintra-cochlear stimulating assembly configured to be implanted in aninner ear of a recipient, wherein the intra-cochlear stimulatingassembly comprises a plurality of stimulating contacts; and one or moreprocessors configured to: obtain, via one or more of the plurality ofstimulating contacts, objective inner ear responses to acousticstimulation at one or more regions of the inner ear, generate, based onthe objective inner ear responses to acoustic stimulation, a mapping ofone or more relationships between the acoustic stimulation and an outputfunctionality of the one or more regions of the inner ear, and generate,based on at least the mapping of one or more relationships between theacoustic stimulation and an output functionality of the one or moreregions of the inner ear, an acoustic prescription for conversion ofsound signals to acoustic stimulation signals for delivery to therecipient.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein in conjunctionwith the accompanying drawings, in which:

FIG. 1A is a schematic diagram of a hearing prosthesis system inaccordance with embodiments presented herein;

FIG. 1B is a block diagram of the hearing prosthesis system of FIG. 1A;

FIGS. 2A, 2B, 2C, and 2D are schematic diagrams illustrating operationof a recipient's inner ear;

FIG. 3 is a schematic diagram illustrating a portion of a recipient'sinner ear;

FIG. 4 is a detailed flowchart illustrating a method in accordance withembodiments presented herein;

FIG. 5A is a graph illustrating measured auditory nerve neurophonic(ANN) outputs and normal/expected auditory nerve neurophonic outputs;

FIG. 5B is a graph illustrating measured outer hair cell (OHC) functionoutputs and normal/expected outer hair cell function outputs;

FIG. 6 is a graph illustrating an example gain function generated inaccordance with embodiments presented herein;

FIG. 7 is a graph illustrating a comparison of hearing thresholdsdetermined from an audiogram and hearing thresholds determined fromobjective measurements in accordance with embodiments presented herein;

FIG. 8 is a graph illustrating a comparison of gain functions determinedfrom an audiogram and gain functions determined from objectivemeasurements in accordance with embodiments presented herein;

FIG. 9 is a block diagram illustrating one arrangement for an externaldevice forming part of an electro-acoustic hearing prosthesis system inaccordance with embodiments presented herein; and

FIG. 10 is a high-level flowchart of a method in accordance withembodiments presented herein.

DETAILED DESCRIPTION

Auditory/hearing prosthesis recipients suffer from different types ofhearing loss (e.g., conductive and/or sensorineural) and/or differentdegrees/severity of hearing loss. However, it is now common for manyhearing prosthesis recipients to retain some residual natural hearingability (residual hearing) after receiving the hearing prosthesis. Forexample, progressive improvements in the design of intra-cochlearelectrode arrays (stimulating assemblies), surgical implantationtechniques, tooling, etc. have enabled atraumatic surgeries whichpreserve at least some of the recipient's fine inner ear structures(e.g., cochlea hair cells) and the natural cochlea function,particularly in the higher frequency regions of the cochlea.

Due, at least in part, to the ability to preserve residual hearing, thenumber of recipients who are candidates for different types ofimplantable hearing prostheses, particularly electro-acoustic hearingprostheses, has continued to expand. Electro-acoustic hearing prosthesesare medical devices that deliver both acoustic stimulation (i.e.,acoustic stimulation signals) and electrical stimulation (i.e.,electrical stimulation signals), possibly simultaneously, to the sameear of a recipient.

The cochlea is “tonotopically mapped,” meaning that regions of thecochlea toward the basal region are responsive to higher frequencysignals, while regions of the cochlea toward apical region areresponsive to lower frequency signals. For example, the proximal end ofthe basal region is generally responsible to 20 kilohertz (kHz) sounds,while the distal end of the apical region is responsive to sounds ataround 200 hertz (Hz). In hearing prosthesis recipients, residualhearing most often is present within the lower frequency ranges (i.e.,the more apical regions of the cochlea) and little or no residualhearing is present in the higher frequency ranges (i.e., the more basalregions of the cochlea). This property of residual hearing is exploitedin electro-acoustic hearing prostheses where the stimulating assembly isinserted into the basal region and is used to deliver electricalstimulation signals to evoke perception of higher frequency soundcomponents, while acoustic stimulation is used to evoke perception ofsound signal components corresponding to the lower frequencies of inputsound signals (as determined from the residual hearing capabilities ofthe implanted ear). The tonotopic region of the cochlea where thestimulation output transitions from the acoustic stimulation to theelectrical stimulation is called the cross-over frequency/frequencyregion.

Electro-acoustic hearing prosthesis recipients typically benefit fromhaving the acoustic stimulation in addition to the electricalstimulation, as the acoustic stimulation adds a more “natural” sound totheir hearing perception over the electrical stimulation signals only inthat ear. The addition of the acoustic stimulation can, in some cases,also provide improved pitch and music perception and/or appreciation, asthe acoustic signals may contain a more salient lower frequency (e.g.,fundamental pitch, F0) representation than is possible with electricalstimulation. Other benefits of electro-acoustic hearing prosthesis mayinclude, for example, improved sound localization, binaural release fromunmasking, the ability to distinguish acoustic signals in a noisyenvironment, etc.

The effectiveness of electro-acoustic and other hearing prosthesesgenerally depends on how well a particular prosthesis is configured or“fit” to the recipient of the particular prosthesis. For instance, the“fitting” of a hearing prosthesis to a recipient, sometimes alsoreferred to as “programming” creates a set of configuration settings,parameters, and other data (collectively and generally “settings”herein) that define the specific operational characteristics of thehearing prosthesis. In the case of electro-acoustic hearing prostheses,fitting determines how the prosthesis operates to convert portions(frequencies and/or frequency ranges) of detected sound signals (sounds)into electrical and acoustic stimulation signals. For example, thefitting process results in the determination of an “acousticprescription” comprising one or more sets of gain functions that areused to map/translate received sound signals into output acousticsimulation levels.

Presented herein are techniques that make use of objective measurements,such as acoustically-evoked inner ear responses, in the fitting processto determine the patient-centric acoustic prescription (gain functions)that are used by an electro-acoustic hearing prosthesis to translatereceived sound signals into output acoustic simulation levels. Morespecifically, in accordance with the techniques presented herein aplurality of acoustically-evoked inner ear responses are obtained froman inner ear of a recipient of an electro-acoustic hearing prosthesis.One or more input/output functions for at least one region of the innerear are determined based on the plurality of acoustically-evoked innerear responses and the one or more input/output functions are, in turn,used to determine one or more gain functions for use by theelectro-acoustic hearing prosthesis.

As described further below, the techniques presented herein create anacoustic prescription (i.e., a set of gain functions), which isprimarily based on personalized measurements/responses of therecipient's inner ear, such as the auditory nerve neurophonic (ANN)and/or cochlear microphonic (CM), to acoustic stimulation signals. Theauditory nerve neurophonic function, when correlated with the acousticstimulation signals, provide a basic input/output function for atonotopic region of the inner ear. This input/output function which istransformed into an acoustic prescription after applying variousloudness rules. In certain embodiments, outer hair cell (OHC) function,as represented by the cochlear microphonic, are also obtained andcorrelated (e.g., compared) with the auditory nerve neurophonic. Inthese embodiments, the correlation of the outer hair cell functionresponses with the auditory nerve neurophonic can usefully identifymismatches which are then used to make further personalized adjustmentsto the prescription. For example, dead regions can be identified andtaken into account, thereby leading to a superior prescription for eachrecipient.

For ease of illustration, embodiments are primarily described hereinwith reference to a hearing prosthesis system that includes anelectro-acoustic hearing prosthesis comprising a cochlear implantportion and a hearing aid portion. However, it is to be appreciated thatthe techniques presented herein may be used with other types of hearingprostheses, such as bi-modal hearing prostheses, electro-acoustichearing prosthesis comprising other types of output devices (e.g.,auditory brainstem stimulators, direct acoustic stimulators, boneconduction devices, etc), etc.

FIGS. 1A and 1B are diagrams of an illustrative hearing prosthesissystem 101 configured to implement the techniques presented herein. Morespecifically, FIGS. 1A and 113 illustrate hearing prosthesis system 101that comprises an electro-acoustic hearing prosthesis 100 and anexternal device 105. The external device 105 is a computing device, suchas a computer (e.g., laptop, desktop, tablet), mobile phone, remotecontrol unit, etc. For ease of description, the external device 105 isdescribed as being a computer.

The implantable electro-acoustic hearing prosthesis 100 includes anexternal component 102 and an internal/implantable component 104. Theexternal component 102 is configured to be directly or indirectlyattached to the body of a recipient, while the implantable component 104is configured to be subcutaneously implanted within the recipient (i.e.,under the skin/tissue 103 of the recipient).

The external component 102 comprises a sound processing unit 110, anexternal coil 106, and, generally, a magnet (not shown in FIG. 1A) fixedrelative to the external coil 106. The external coil 106 is connected tothe sound processing unit 110 via a cable 134. The sound processing unit110 comprises one or more sound input elements 108 (e.g., microphones,audio input ports, cable ports, telecoils, a wireless transceiver,etc.), a wireless transceiver 109, a sound processor 112, a power source116, and a measurement module 118. The sound processing unit 110 may be,for example, a behind-the-ear (BTE) sound processing unit, a body-wornsound processing unit, a button sound processing unit, etc.

Connected to the sound processing unit 110 (e.g., via a cable 135) is ahearing aid component 141. The hearing aid component 141 includes areceiver 142 (FIG. 1B) that may be, for example, positioned in or nearthe recipient's outer ear. The receiver 142 is an acoustic transducerthat is configured to deliver acoustic signals (acoustic stimulationsignals) to the recipient's inner ear via the outer ear, ear canal, andthe middle ear.

As shown in FIG. 1B, the implantable component 104 comprises an implantbody (main module) 122, a lead region 124, and an elongateintra-cochlear stimulating assembly 126. The implant body 122 generallycomprises a hermetically-sealed housing 128 in which an internaltransceiver unit (transceiver) 130 and a stimulator unit 132 aredisposed. The implant body 122 also includes an internal/implantablecoil 136 that is generally external to the housing 128, but which isconnected to the transceiver 130 via a hermetic feedthrough (not shownin FIG. 1B). Implantable coil 136 is typically a wire antenna coilcomprised of multiple turns of electrically insulated single-strand ormulti-strand platinum or gold wire. The electrical insulation ofimplantable coil 136 is provided by a flexible molding (e.g., siliconemolding), which is not shown in FIG. 1B. Generally, a magnet is fixedrelative to the implantable coil 136.

Elongate stimulating assembly 126 is configured to be at least partiallyimplanted in the recipient's cochlea 120 (FIG. 1A) and includes aplurality of longitudinally spaced intra-cochlear electrical stimulatingcontacts (electrodes) 138 that collectively form a contact array 140 fordelivery of electrical stimulation (current) to the recipient's cochlea.

Stimulating assembly 126 extends through an opening 121 in the cochlea(e.g., cochleostomy, the round window, etc.) and has a proximal endconnected to stimulator unit 132 via lead region 124 and a hermeticfeedthrough (not shown in FIG. 1B). Lead region 124 includes a pluralityof conductors (wires) that electrically couple the electrodes 138 to thestimulator unit 132.

Returning to external component 102, the sound input element(s) 108 areconfigured to detect/receive input sound signals and to generateelectrical input signals therefrom. The sound processor 112 isconfigured execute sound processing and coding to convert the electricalinput signals received from the sound input elements into output signalsthat represent acoustic and/or electric (current) stimulation fordelivery to the recipient. That is, as noted, the electro-acoustichearing prosthesis 100 operates to evoke perception by the recipient ofsound signals received by the sound input elements 108 through thedelivery of one or both of electrical stimulation signals and acousticstimulation signals to the recipient. As such, depending on a variety offactors, the sound processor 112 is configured to convert the electricalinput signals received from the sound input elements into a first set ofoutput signals representative of electrical stimulation and/or into asecond set of output signals representative of acoustic stimulation. Theoutput signals representative of electrical stimulation are representedin FIG. 1B by arrow 115, while the output signals representative ofacoustic stimulation are represented in FIG. 1B by arrow 117.

The output signals 115 are, in the examples of FIGS. 1A and 1B, encodeddata signals that are sent to the implantable component 104 via externalcoil 106. More specifically, the magnets fixed relative to the externalcoil 106 and the implantable coil 136 facilitate the operationalalignment of the external coil 106 with the implantable coil 136. Thisoperational alignment of the coils enables the external coil 106 totransmit the encoded data signals, as well as power signals receivedfrom power source 116, to the implantable coil 136. In certain examples,external coil 106 transmits the signals to implantable coil 136 via aradio frequency (RF) link. However, various other types of energytransfer, such as infrared (IR), electromagnetic, capacitive andinductive transfer, may be used to transfer the power and/or data froman external component to an electro-acoustic hearing prosthesis and, assuch, FIG. 1B illustrates only one example arrangement.

In general, the encoded data and power signals are received at thetransceiver 130 and are provided to the stimulator unit 132. Thestimulator unit 132 is configured to utilize the encoded data signals togenerate electrical stimulation signals (e.g., current signals) fordelivery to the recipient's cochlea via one or more stimulating contacts138 in this way, electro-acoustic hearing prosthesis 100 electricallystimulates the recipient's auditory nerve cells, bypassing absent ordefective hair cells that normally transduce acoustic vibrations intoneural activity, in a manner that causes the recipient to perceive oneor more components of the received sound signals.

As noted above, it is common for hearing prosthesis recipients to retainat least part of this normal hearing functionality (i.e., retain atleast one residual hearing). Therefore, the cochlea of a hearingprosthesis recipient can be acoustically stimulated upon delivery of asound signal to the recipient's outer ear. In the example of FIGS. 1Aand 1B, the receiver 142 is used to provide the acoustic stimulation.That is, the receiver 142 is configured to utilize the output signals117 to generate acoustic stimulation signals that are provided to therecipient's cochlea via the middle ear bones and oval window, therebycreating waves of fluid motion of the perilymph within the cochlea.

Although FIGS. 1A and 1B illustrate the use of a receiver 142 to deliveracoustic stimulation to the recipient, it is to be appreciated thatother types of devices may be used in other embodiments. It is also tobe appreciated that embodiments of the present invention may beimplemented in other hearing prostheses and other arrangements that thatshown in FIGS. 1A and 1B. For example, it is to be appreciated thatembodiments of the present invention may be implemented infully-implantable hearing prostheses in which the sound processor, powersupply, etc. are all implanted within a recipient so that the hearingprosthesis may operate, for at least a period of time, without thepresence of an external component.

As noted, the electro-acoustic hearing prosthesis 100 also comprises themeasurement module 118. As described further below, the measurementmodule 118 is configured to obtain one or more inner earpotentials/responses measured in-situ from the recipient's inner ear. Asused herein, “inner ear potentials” refer to any voltage potentialassociated with either the electrical properties of the inner ear or itsphysiological function and/or potentials obtained via measurements atthe inner ear. Potentials of a physiological nature (i.e., potentialsrelating to the physiological function of the inner ear), includeacoustically-induced responses/potentials (e.g., electrocochleography(ECoG) responses) and electrically-induced responses/potentials (e.g.,electrically evoked compound action potential (ECAP) responses. Otherpotentials of a physiological nature are referred to herein as higherevoked potentials, which are potentials related to the brainstem andauditory cortex, inclusive of the electrical auditory brainstemresponses (EABR), the middle latency response, and cortical responses.Potentials of a physiological nature are sometimes referred to herein as“physiological potentials.” Potentials of electrical nature (i.e.,potentials relating to the electrical properties of the inner ear itselfor intra-cochlear contacts) include voltage tomography responses,measured impedances (bulk and interface), and/or other forms ofelectrode (stimulating contact) voltage measurements. Potentials ofelectrical nature are sometimes referred to herein as “physiologicalelectrical potentials.”

As described further below, certain embodiments of the present inventionmake use of acoustically-evoked inner ear responses, such as ECoGresponses, that are generated in a recipient's inner ear in response tothe delivery of acoustic stimulation to the cochlea. A captured set ofacoustically-evoked inner ear response may include a plurality ofdifferent stimulus related potentials, such as the cochlear microphonic(CM), the cochlear summating potential (SP), the auditory nerveneurophonic (ANN), and the auditory nerve or Compound Action Potential(CAP), which are measured independently or in various combinations.

The summating potential is the direct current (DC) response of the outerhair cells of the organ of Corti as they move in conjunction with thebasilar membrane (i.e., reflects the time-displacement pattern of thecochlear partition in response to the stimulus envelope). The summatingpotential is the stimulus-related potential of the cochlea and can beseen as a DC (unidirectional) shift in the cochlear microphonicbaseline. The direction of this shift (i.e., positive or negative) isdependent on a complex interaction between stimulus parameters and thelocation of the recording electrode(s).

The cochlear microphonic is a fluctuating voltage that mirrors thewaveform of the acoustic stimulus at low, moderate, and high levels ofacoustic stimulation. The cochlear microphonic is generated by the outerhair cells (OHCs) of the organ of Corti and is dependent on theproximity of the recording electrode(s) to the stimulated hair cells andthe basilar membrane. In general, the cochlear microphonic isproportional to the displacement of the basilar membrane by thetravelling wave phenomena and reflects/represents the outer hair cellfunction.

More specifically, the outer hair cells possess electromotility, aquality that can generate rapid and significant forces on the basilarmembrane by the cell structure lengthening and contracting with sensoryinput from the auditory nerve. As shown in FIGS. 2A and 2B, thiselectromotility permits the cochlea to serve as an amplifier for sounds,thereby providing a non-linear compressive nature for input sounds.However, as shown in FIGS. 2C and 2D, the cochlea amplifier input/outputfunction across a frequency can be compromised by a hearing impairment.

The signal throughput from the outer hair cell activity to the innerhair cell activity can be further compromised by the synapticconnections to the auditory nerve, as characterized by the auditorynerve neurophonic (ANN). The auditory nerve neurophonic is a signalrecorded from the auditory nerve in response to the acoustic stimulationsignals and represents the auditory nerve neurophonic function.

The auditory nerve Action Potential represents the summed response ofthe synchronous firing of the nerve fibers in response to the acousticstimuli, and it appears as an alternating current voltage. The auditorynerve Action Potential is characterized by a series of brief,predominantly negative peaks, including a first negative peak (N1) andsecond negative peak (N2). The auditory nerve Action Potential alsoincludes a magnitude and a latency. The magnitude of the auditory nerveAction Potential reflects the number of fibers that are firing, whilethe latency of the auditory nerve Action Potential is measured as thetime between the onset and the first negative peak (N1).

FIG. 3 is a schematic diagram illustrating the physiology of a portionof recipient's inner ear. FIG. 3 has also been labeled to illustratewhere each of the cochlear microphonic (CM), the cochlear summatingpotential (SP), the auditory nerve neurophonic (ANN), and the auditorynerve or Compound Action Potential (CAP) are generated in the inner ear.

Returning to examples of FIGs. lA and 1B, the measurement module 118 isconfigured to provide the obtained inner ear potentials to the computer105. In one embodiment, the computer 105 includes a wireless transceiver111 that is configured to wirelessly communicate with the wirelesstransceiver 109 of the sound processing unit 110 to obtain/receive theinner ear potentials. In other embodiments, the computer 105 isphysically connected to the sound processing unit 110 (e.g., via a portor interface of the sound processing unit and one or more interfaces ofthe computer) so as to receive the inner ear potentials over a wiredconnection. As described further below, upon obtaining the inner earpotentials, an objective acoustic prescription module 144 of thecomputer 105 is configured to use the inner ear potentials to generateone or more input/output functions for tonotopic regions of the cochlea.Using these input/output functions, as well as one or more loudnessrules, the objective acoustic prescription module 144 generates anacoustic prescription (e.g., one or more sets of gain functions) for useby the electro-acoustic hearing prosthesis 100 to convert sound signalcomponents into acoustic stimulation signals. That is, once generated,the acoustic prescription is provided to, and subsequently used by, theelectro-acoustic hearing prosthesis 100

The objective generation of the acoustic prescription improves theoperation of the electro-acoustic hearing prosthesis 100 and optimizes(e.g., personalizes) the gain functions for the recipient. That is, anacoustic prescription created using the techniques presented herein ishighly personalized for the recipient due to the close and directconnections with the unique auditory biology of each recipient, and isalso independent of the physical characteristics of the ear canal whichcan vary from recipient to recipient and which can lead to errors inconventional techniques for determining gain functions (i.e., does notrequire third party real-ear verification hardware for fitting qualitycontrol as required in conventional fitting practices).

In addition, an acoustic prescription created using the techniques canbe substantially, and possibly fully, automated and relies upon minimalsignificant subjective feedback from the recipient (i.e., minimalinteraction with the recipient). This makes the techniques presentedsuitable for children and or other recipients that may be unable toprovide reliable subjective feedback. Moreover, certain embodimentsfacilitate detection of, and accommodation for, dead regions and otherphysiological abnormalities.

FIGS. 1A and 1B illustrate an arrangement in which the objectiveacoustic prescription module 144 is located at an external device 105.It is also to be appreciated that the objective acoustic prescriptionmodule 144 may implemented as part of the electro-acoustic hearingprosthesis 100 (e.g., as part of sound processing unit 110).

Furthermore, FIGS. 1A and 1B illustrate an arrangement in which theelectro-acoustic hearing prosthesis 100 includes an external component102. However, it is to be appreciated that embodiments of the presentinvention may be implemented in hearing prostheses having alternativearrangements. Similarly, FIGS. 1A and 1B illustrate the use of areceiver 142 to deliver acoustic stimulation to obtainacoustically-evoked inner ear responses. However, embodiments of thepresent invention may be implemented in other hearing prostheses thatdeliver stimulation in a different manner to evoke anacoustically-induced potential measurement (e.g., bone conductiondevices or direct acoustic stimulators that deliver vibration to thecause pressure changes within the cochlea fluid).

FIG. 4 is a flowchart illustrating a method 150 in accordance withembodiments presented herein. For ease of illustration, the method 150of FIG. 4 will be described with reference to the electro-acoustichearing prosthesis system 101 of FIGS. 1A and 1B.

Method 150 begins at 152 where an audiogram measurement of therecipient's cochlea 140 is performed in order to record the recipient'sresidual hearing (i.e., to determine the frequency and/or frequencyrange where the recipient's residual hearing begins). An audiogrammeasurement refers to a behavioral hearing test, sometimes referred toas audiometry, which generates an audiogram. The behavioral testinvolves the delivery of different tones, presented at a specificfrequency (pitch) and intensity (loudness), to the recipient's cochleaand the recording of the recipient's subjective responses. The resultingaudiogram is a graph that illustrates the audible threshold forstandardized frequencies as measured by an audiometer. In general,audiograms are set out with frequency in Hertz (Hz) on the horizontal(X) axis, most commonly on a logarithmic scale, and a linear decibelsHearing Level (dBHL) scale on the vertical (Y) axis. In certainarrangements, the recipient's threshold of hearing is plotted relativeto a standardized curve that represents ‘normal’ hearing, in dBHL. Theaudiogram is used to determine the frequency and threshold of hearingfor the recipient's cochlea.

At 154, the objective acoustic prescription module 144 obtains aplurality of acoustically-evoked inner ear responses at a selectedsampling frequency. More specifically, acoustic stimulation signals(e.g., acoustic tones pure tones) are delivered, at the samplingfrequency, to the recipient's outer ear using, for example, the receiver142. The acoustic stimulation signals delivered by the receiver 142cause displacement waveforms that travel along the basilar membrane andwhich rise to potentials. Therefore, in response to the deliveredacoustic signals, one or more of the stimulating contacts 138 and theintegrated amplifier(s) 143 of the cochlear implant capture one or morewindows of the evoked activity (i.e., perform ECoG measurements) togenerate acoustically-evoked inner ear responses (e.g., ECoG responses),which are generally represented in FIG. 1B by arrow 145, are transmittedback to the sound processing unit 110 and then forwarded to the externaldevice 105.

The acoustic stimulation signals delivered at 154 have acertain/selected frequency, referred to as the sampling frequency. Thesampling frequency remains constant, but the level/amplitude of theacoustic stimulation signals is changed to obtain a plurality ofdifferent sets of responses. In other words, the operations at 154include the delivery of acoustic stimulation signals at incrementaladjusted (e.g., incrementally increasing) amplitudes, but at a constantfrequency.

As noted above, a recipient's cochlea is tonotopically mapped such thatregions of the cochlea toward the basal region are responsive to higherfrequency signals, while regions of cochlea toward the apical region areresponsive to lower frequency signals. Also as noted above, in anelectro-acoustic hearing prosthesis, such as prosthesis 100, acousticstimulation is used to stimulate the frequencies below the cross-overfrequency. As such, in accordance with the embodiments of FIG. 4 , thesampling frequency is a frequency at which acoustic stimulation signalsare expected to be delivered to the recipient (i.e., a frequency belowthe cross-over frequency).

At 156, the objective acoustic prescription module 144 is configured touse the plurality of inner ear responses obtained at 154 to determineone or more input/output (I/O) functions for the tonotopic region of thecochlea that corresponds to the sampling frequency, sometimes referredto herein as the sampled cochlea region. In general, the one or moreinput/output functions generated at 156 represent a mapping of one ormore relationships between the acoustic signals delivered to the cochleaand an output functionality of the one or more regions of the inner ear(e.g., measured auditory nerve neurophonics). In certain embodiments, atleast one input/output function is generated based on an analysis ofmeasured auditory nerve neurophonics in relation to attributes of thedelivered acoustic stimulation signals. In further embodiments, at leastone output function is generated based on an analysis of measuredcochlear microphonics (outer hair cell function) in relation to theattributes (e.g., amplitude) of the delivered acoustic stimulationsignals.

The I/O functions may be calculated/determined in a number of differentmanners in either the time or frequency domain whereby both the inputand output measures are consistent and a measurement of the signalamplitude or power is made. In one example, a time-domain RMS value ofthe input and output signal may be determined as the I/O function.

FIGS. 5A and 5B are graphs illustrating further details of exampleauditory nerve neurophonic outputs and outer hair cell outputs,respectively, that may be used to determine input/output functions inaccordance with embodiments presented. More specifically, the graph ofFIG. 5A includes a first trace 151 representing the auditory nerveneurophonic outputs determined from a recipient's inner ear responses toan acoustic pure tone having an amplitude that is increased from 0 dBSPL to 100 dB SPL. The graph of FIG. 5A also includes a second trace 153that illustrates auditory nerve neurophonic outputs that are associatedwith a normal/normative inner ear. That is, trace 153 represents theoutput that may be expected from a typical inner ear, while trace 151represents the outputs that are associated with the inner ear of aspecific recipient. The horizontal (X) axis of the graph shown in FIG.5A represents the increasing level of the acoustic pure tone (i.e., thesignal that evokes the corresponding auditory nerve neurophonicresponses). The vertical (Y) axis represents the normalized outputs (nounits) for the auditory nerve neurophonic.

The graph of FIG. 5B includes a first trace 155 representing the outerhair cell outputs determined from a recipient's inner ear responses toan acoustic pure tone having an amplitude that is increased from 0 dBSPL to 100 dB SPL. The graph of FIG. 5B also includes a second trace 157that illustrates outer hair cell outputs that are associated with anormal/normative inner ear. That is, trace 157 represents the outputthat may be expected from a typical inner ear, while trace 155represents the outputs that are associated with the inner ear of aspecific recipient. Similar to FIG. 5A, the horizontal axis of the graphshown in FIG. 5B represents the increasing level of the acoustic puretone, while the vertical axis represents the normalized outputs (nounits) for the outer hair cell outputs.

Returning to FIG. 4 , at 158 the objective acoustic prescription module144 analyzes the one or more input/output functions generated for thesampled cochlea region for physiological abnormalities (e.g., auditorynerve neuropathy, the presence of a dead region, etc.). Morespecifically, at 158 the objective acoustic prescription module 144performs a diagnostic operation to determine, based on the one or moreinput/output functions, whether the sampled cochlea region isfunctioning properly (i.e., as expected) in response to acousticstimulation. If the sampled cochlea region is functioning improperly,then the objective acoustic prescription module 144 may operate todetermine why the output is not proper (i.e., determine or classify thecause). In certain embodiments, the analysis for physiologicalabnormalities is based on an analysis of the auditory nerve neurophonicfunction relative to the outer hair cell function.

In certain examples, the abnormalities are detected by any mismatchbetween the expected behavior of the CM and the ANN (e.g., relative toanother, relative to normative data, etc.). The process of detectingmismatches can include, in certain examples, a difference measure ineither the time or the frequency domain. If the difference measureexceeds a particular tolerance, then the response is classified asabnormal either at a particular frequency or globally.

Physiological abnormalities, if present, can impact the gain that isapplied to acoustic stimulation signals at the sampling frequency. Forexample, if a dead region (i.e., a region where the nerve cells are deadand non-responsive) is identified at a particular frequency, then nooutput is produced and it is ineffective to amplify sounds at thatfrequency. Therefore, as described below, identified physiologicalabnormalities can be used is refine the gain functions, accordinglyfurther personalizing the acoustic prescription for the recipient.

As noted above, a recipient's cochlea is tonotopically mapped andacoustic stimulation is used to stimulate the frequencies below thecross-over frequency. As such, a gain function forming part of anacoustic prescription should cover a number of frequencies below thecross-over frequency. Therefore, a determination is made at 160 as towhether or not input/output functions have been determined for allcochlea regions corresponding to each of a plurality of selectedfrequencies, where the plurality of selected frequencies are a number offrequencies at which acoustic stimulation signals are to be delivered tothe recipient (i.e., a set of frequencies for which gains are neededduring acoustic stimulation).

If it is determined at 160 that one or more input/output functions havenot been determined for cochlea regions corresponding to each of theplurality of selected frequencies, then at 162 the sampling frequency ischanged/advanced to a next one of the selected frequencies. Theoperations of 154, 156, 160, and 162 are then repeated until it isdetermined at 160 that one or more input/output functions have beendetermined for cochlea regions corresponding to all of the plurality ofselected frequencies.

Once one or more input/output functions have been determined for cochlearegions corresponding to all of the plurality of selected frequencies,then method 150 proceeds to 164 where one or more loudness models/rulesare applied across the plurality of selected frequencies. Morespecifically, the audiogram for the receipient (i.e., generated at 152)is employed along with the one or more input/output functions and thephysiological abnormalities, if present, as inputs to a loudness model(e.g., set of loudness rules) that are, in general, intended to ensurethat the fitting gain maximizes speech intelligibility at the same timeas keeping overall loudness no greater than that of a normal hearingperson. The one or more input/output functions acquired using theobjective measures are peripheral to the cochlea function and, as such,generally do not account for the the mid-level and the higher levelprocessing of the recipient's auditory system. These higher levels ofauditory processing introduce loudness changes that should be accountedfor when setting the gain functions so as to ensure both intelligibilityand proper loudness are preserved.

Stated differently, at 164 the input/output functions, audiogram, andthe physiological abnormalities are used as inputs to a system, executedat objective acoustic prescription module 144, that accounts for whathappens at a higher cognitive level of hearing (i.e., the mid-brainelements, the auditory cortex, etc.). The loudness models can be used tomap the electrophysiological measurements to how they might be perceivedat the higher cognitive level (the cortex).

At 166, following application of the loudness models/rules, one or moregain functions are derived for use in converting sound signal componentsin acoustic stimulation signals. That is, the one or more gain functionsare generated based on the outputs generated as a result of theapplication of the loudness models/rules to the input/output functions,audiogram, and the physiological abnormalities. FIG. 6 is a graphillustrating an example gain function 170 corresponding to sound signalsreceived at an input level of 65 dB SPL. As shown, the gain applieddecreases as the frequency increases (horizontal axis), where thevertical axis represents the normalized gain (no units). The gainfunction 170 represents an example of device configuration settingsgenerated by the objective acoustic prescription module 144 (i.e., theresult is a derivation of gain settings for the acoustic stimulation)and implemented by the electro-acoustic hearing prosthesis 100. Incertain examples, different gain functions may be derived for differentsound signal levels (i.e., an acoustic prescription may comprise a setof multiple different gain functions).

FIG. 4 has been described with reference to the use of the input/outputfunctions, audiogram, and the physiological abnormalities are inputs tothe loudness models/rules (i.e., some system, executed at objectiveacoustic prescription module 144, that accounts for what happens at ahigher cognitive level of hearing). It is to be appreciated that ismerely illustrative and that only a subset of the input/outputfunctions, audiogram, and the physiological abnormalities may be usedinputs to the loudness models/rules. For example, in certainembodiments, only the input/output functions may be employed as inputsto the loudness models/rules to configure the acoustic hearingprescription. Such embodiments would permit those who cannot providebehavioral feedback with a completely subjective fitting method. Furtherto this, for such a population, the method may be complemented by theuse of other objective measures such as higher evoked potentials such asthe EABR and cortical response, sometimes employed for fitting thosewithout the ability to provide behavioral feedback.

It is also to be appreciated that the input/output functions themselvesmay be employed, without the loudness models, to configure a recipient'sacoustic hearing prescription (i.e., to determine one or more gainfunctions for use by the electro-acoustic hearing prosthesis inconversion of sound signals to acoustic stimulation signals for deliveryto the recipient). Such techniques could be refined to include theloudness models and/or other information, such as the audiogram, thephysiological abnormalities, etc.

FIG. 7 is a graph illustrating a comparison of the differences inhearing threshold resulting from a conventional audiogram approachversus approaches in accordance with the embodiments presented herein,both for a “normal” physiology and for an “abnormal” physiology. In FIG.7 , the horizontal axis represents increasing frequency, while thevertical axis represents determined hearing loss.

FIG. 7 includes an audiogram trace 172 that illustrates audiogramhearing thresholds determined using an audiogram measurement. As notedabove, the audiogram captures the recipient's behavioral hearingthresholds across frequency. As shown, the audiogram trace 172 issteeply sloped in the lower frequencies and indicates a high frequencyhearing loss. This type of hearing loss is typical of a recipient whomay be a candidate for an electro-acoustic hearing prosthesis(pre-implantation or post-implantation).

Also shown in FIG. 7 are traces 174, 176, and 178. Traces 174 and 176correspond to the thresholds of the cochloear microphonic for normal andabnormal hearing, respectively, measured in-situ. Trace 178 correspondsto the thresholds of the auditory nerve neurophonic measured in-situ. Asshown the profiles of the cochlear microphonic for normal hearing (174)and for the auditory nerve neurophonic (178) are similar to each other,but are different from that of the audiogram (172).

The normal cochlear microphonic (174) is the classification resultingfrom the comparison of the profiles of the auditory nerve neurophonicand cochlear microphonic, given these track together closely acrossfrequency. The abnormal cochlear microphonic (176) is an alternativeclassification resulting again from the comparison of the profiles ofthe auditory nerve neurophonic and cochlear microphonic. In thisinstance the cochlear microphonic deviates away from the auditory nerveneurophonic, indicating there is an absence or small population of outerhair cells (OHCs) in this region of the cochlea. The presence of alarger auditory nerve neurophonic in these regions of the cochlea (e.g.,750-2000 Hz) suggests a phenomenon called ‘off-frequency hearing,’whereby the spread of excitation of regions not associated with thedelivered frequency give rise to the behavioral threshold. Thephysiological explanation of this phenomena is often referred to as a“dead region.”

FIG. 8 is a graph illustrating gains calculated for an input level of 50dBHL. In FIG. 8 , the horizontal axis represents increasing frequency,while the vertical axis represents the gain values that would beprogrammed into a hearing prosthesis for the given frequency.

FIG. 8 includes an audiogram trace 182 illustrating gain valuesgenerated based only on an audiogram measurement, a normal cochlearmicrophonic trace 184 illustrating gain values generated based oncochlear microphonics classified as normal, and an abnormal cochlearmicrophonic trace 186 illustrating gain values generated based oncochlear microphonics classified as abnormal. As shown, each of the gainfunctions 184 and 186 are different to that of the conventionalaudiogram approach represented by 182. In FIG. 8 , locations where thegains are set to zero represent the stop point of the acoustic fitting(i.e., gain of zero implies there is no acoustic signal presented atthis frequency to the cochlea).

A comparison of the audiogram trace 182 versus the normal cochlearmicrophonic trace 184 reveals that, due to the cochlear microphonicanalysis, one additional frequency channel is added to the recipient'sgain profile. The abnormal cochlear microphonic trace 186 is differentfrom the normal cochlear microphonic trace 184 because a comparison ofthe auditory nerve neurophonic and the cochlear microphonic has revealedthe presence of a dead region at certain frequencies of the cochlea.This has translated to these frequencies not being fitted resulting in alarge difference between the two fittings (i.e., between 184 and 186).The clinical rationale for not fitting frequencies associated with adead region is that there is a risk other parts of the cochlea mayreceive this information (off-frequency) and there is a risk ofinformation being either masked or degraded if these frequencies areamplified. It is not possible to determine such dead regions from theaudiogram alone.

FIG. 9 is a block diagram illustrating further details of onearrangement for external device 105 forming part of an electro-acoustichearing prosthesis system in accordance with embodiments presentedherein. As noted above, external device 105 may be, for example, acomputing device, such as a remote assistant for the hearing prosthesis,computer (e.g., laptop, desktop, tablet), mobile phone, etc., or otherdevice configured for communication with an electro-acoustic hearingprosthesis, such as prosthesis 100 of FIGS. 1A and 1B.

Referring specifically to the arrangement of FIG. 9 , the externaldevice 105 comprises one or more communication interfaces 185, one ormore processors 188, a display screen 190, a user interface 192, amemory 194, and a speaker 198. The memory 194 includes objectiveacoustic prescription logic 196.

The one or more communications interfaces 185 comprise one or moreelements for wired or wireless communication with a hearing prosthesis.The communications interfaces 186 may comprise, for example, ashort-range wireless transceiver 111, such as a Bluetooth® transceiverthat communicates using short-wavelength Ultra High Frequency (UHF)radio waves in the industrial, scientific and medical (ISM) band from2.4 to 2.485 gigahertz (GHz). Bluetooth® is a registered trademark ownedby the Bluetooth® SIG. The communications interfaces 186 may also oralternatively comprise a telecommunications interface, a wireless localarea network interface, one or more network interface ports, aradio-frequency (RF) coil and RF transceiver, etc.

The display screen 190 is an output device, such as a liquid crystaldisplay (LCD), for presentation of visual information to a user (e.g.,surgeon). The user interface 192 may take many different forms and mayinclude, for example, a keypad, keyboard, mouse, touchscreen, displayscreen, etc. In certain embodiments, the display screen 190 and userinterface 190 are integrated to form a touch-screen display.

Memory 194 may comprise one or more tangible (non-transitory) computerreadable storage media, such as read only memory (ROM), random accessmemory (RAM), magnetic disk storage media devices, optical storage mediadevices, flash memory devices, electrical, optical, or otherphysical/tangible memory storage devices. The one or more processors 188are, for example, microprocessors or microcontrollers that executeinstructions for the objective acoustic prescription logic 196 stored inmemory 194. That is, in one form, the objective acoustic prescriptionmodule 144 is implemented as software, sometimes referred to herein asobjective acoustic prescription software or logic 196, at externaldevice 105. Therefore, when the objective acoustic prescription logic196 is executed by the processors 188, the external device 105 isoperable to perform the operations described herein with reference toobjective acoustic prescription module 144.

FIG. 9 illustrates a specific software implementation for objectiveacoustic prescription module 144 that makes use of onboard digitalsignal processors (DSPs) or microprocessors. However, it is to beappreciated that objective acoustic prescription module 144 may haveother arrangements. For example, objective acoustic prescription module144 may be partially or fully implemented with digital logic gates inone or more application-specific integrated circuits (ASICs).Alternatively, the objective acoustic prescription module 144 may beintegrated in the electro-acoustic hearing prosthesis 100 (e.g., insound processing unit 110).

FIG. 10 is a flowchart of a method 191 in accordance with embodimentspresented herein. Method 191 begins at 193 where a plurality ofacoustically-evoked inner ear responses is obtained from an inner ear ofa recipient of an electro-acoustic hearing prosthesis. At 195, based onthe plurality of acoustically-evoked inner ear responses, one or moreinput/output functions are determined for at least one region of theinner ear. At 197, based on at least the one or more input/outputfunctions, one or more gain functions are determined for use by theelectro-acoustic hearing prosthesis in conversion of sound signals toacoustic stimulation signals for delivery to the recipient.

It is to be appreciated that the embodiments presented herein are notmutually exclusive.

The invention described and claimed herein is not to be limited in scopeby the specific preferred embodiments herein disclosed, since theseembodiments are intended as illustrations, and not limitations, ofseveral aspects of the invention. Any equivalent embodiments areintended to be within the scope of this invention. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

1.-20. (canceled)
 21. A method, comprising: delivering one or more setsof acoustic stimulation signals to an inner ear of a recipient of amedical device; obtaining, in response to the one or more sets ofacoustic stimulation signals, at least one measure of outer hair cellfunction from a tonotopic region of the inner ear of the recipient;obtaining, in response to the one or more sets of acoustic stimulationsignals, at least one measure of auditory nerve function from thetonotopic region of the inner ear of the recipient; comparing a valueassociated with the at least one measure of auditory nerve function to avalue associated with the at least one measure of outer hair cellfunction to obtain a comparison value; and analyzing the at least onemeasure of auditory nerve function relative to the at least one measureof outer hair cell function to determine whether a region of the innerear has a physiological abnormality.
 22. The method of claim 21, whereinthe tonotopic region is tonotopically mapped to a cross-over frequencyfor the recipient.
 23. The method of claim 21, wherein analyzing the atleast one measure of auditory nerve function relative to the at leastone measure of outer hair cell function comprises: determining whetherthe at least one measure of auditory nerve function differs from anexpected measure of auditory nerve function for the tonotopic region theinner ear; determining whether the at least one measure of outer haircell function differs from an expected measure of outer hair cellfunction for the tonotopic region the inner ear; and analyzing anydifferences between the at least one measure of auditory nerve functionand the expected measure of auditory nerve function relative to anydifferences between the at least one measure of outer hair cell functionand the expected measure of outer hair cell function.
 24. The method ofclaim 21, wherein obtaining the at least one measure of outer hair cellfunction from the tonotopic region of the inner ear of the recipientcomprises: obtaining at least one cochlear microphonic from thetonotopic region of the inner ear of the recipient.
 25. The method ofclaim 21, wherein obtaining the at least one measure of auditory nervefunction from the tonotopic region of the inner ear of the recipientcomprises: obtaining at least one auditory nerve neurophonic from thetonotopic region of the inner ear of the recipient.
 26. The method ofclaim 21, further comprising: generating, based on the comparison value,an acoustic prescription for the recipient for frequencies below afrequency corresponding to the tonotopic region.
 27. The method of claim26, further comprising: identifying a presence of a physiologicalabnormality at the tonotopic region; and identifying a type of thephysiological abnormality present at the tonotopic region.
 28. Themethod of claim 21, wherein analyzing the at least one measure ofauditory nerve function relative to the at least one measure of outerhair cell function: analyzing the at least one measure of auditory nervefunction relative to the at least one measure of outer hair cellfunction to determine whether the tonotopic region of the inner ear isfunctioning, in response to the one or more sets of acoustic stimulationsignals, in accordance with at least one predetermined expectation. 29.The method of claim 21, wherein generating, based on the comparisonvalue, an acoustic prescription for the recipient comprises:determining, based on the comparison value, at least one input/outputfor a region of the inner ear.
 30. The method of claim 21, whereingenerating, based on the comparison value, an acoustic prescription forthe recipient comprises: determining, based on the comparison value, oneor more gain functions for a region of the inner ear.
 31. The method ofclaim 30, further comprising: obtaining an audiogram generated for theinner ear of the recipient; and determining the one or more gainfunctions based on the comparison value and based on the audiogramgenerated for the inner ear of the recipient.
 32. The method of claim21, wherein delivering one or more sets of acoustic stimulation signalsto an inner ear of a recipient of a medical device comprises: deliveringacoustic stimulation signals at a selected and substantially constantfrequency while incrementally adjusting an amplitude of the acousticstimulation signals.
 33. An apparatus, comprising: a memory; and one ormore processors configured to: obtain at least one cochlear microphonicevoked from a tonotopic region of an inner ear of a recipient of ahearing prosthesis, obtain at least one auditory nerve neurophonicevoked from the tonotopic region of the inner ear of the recipient,determine whether the at least one auditory nerve neurophonic differsfrom an expected auditory nerve neurophonic for the tonotopic region theinner ear; determine whether the at least one cochlear microphonicdiffers from an expected cochlear microphonic for the tonotopic regionthe inner ear; correlate any differences between the at least oneauditory nerve neurophonic and the expected auditory nerve neurophonicwith any differences between the at least one cochlear microphonic andthe expected cochlear microphonic to obtain a correlation value; andgenerate, based on the correlation value, an acoustic prescription forthe recipient for frequencies below a frequency at which residualhearing for the recipient begins.
 34. The apparatus of claim 33, whereinthe tonotopic region is tonotopically mapped to a cross-over frequencyfor the recipient.
 35. The apparatus of claim 33, wherein the one ormore processors are further configured to: determine, based on thecorrelation value, at least one input/output for a region of the innerear.
 36. The apparatus of claim 33, wherein the one or more processorsare further configured to: determine, based on the correlation value,one or more gain functions for a region of the inner ear.
 37. Theapparatus of claim 36, wherein the one or more processors are furtherconfigured to: obtain an audiogram generated for the inner ear of therecipient; and determine the one or more gain functions based on thecorrelation value and based on the audiogram generated for the inner earof the recipient.
 38. One or more non-transitory computer readablestorage media encoded with instructions that, when executed by one ormore processors, cause the one or more processors to: obtain at leastone measure of outer hair cell function from a tonotopic region of aninner ear of a recipient of a hearing prosthesis; obtain at least onemeasure of auditory nerve function from the tonotopic region of theinner ear of the recipient, wherein the at least one measure of outerhair cell function and the least one measure of auditory nerve functionare evoked in response to acoustic stimulation signals delivered to theinner ear; compare a value associated with the at least one measure ofauditory nerve function to a value associated with the at least onemeasure of outer hair cell function to obtain a comparison result; andgenerate, based on the comparison result, an acoustic prescription forthe recipient for frequencies below a region of the inner ear where astimulation output of the hearing prosthesis transitions from acousticstimulation to electrical stimulation.
 39. The non-transitory computerreadable storage media of claim 38, wherein the instructions operable tocompare the value associated with the at least one measure of auditorynerve function to the value associated with the at least one measure ofouter hair cell function comprise instructions operable to: determinewhether the at least one measure of auditory nerve function differs froman expected measure of auditory nerve function for the tonotopic regionthe inner ear; determine whether the at least one measure of outer haircell function differs from an expected measure of outer hair cellfunction for the tonotopic region the inner ear; and analyze anydifferences between the at least one measure of auditory nerve functionand the expected measure of auditory nerve function relative to anydifferences between the at least one measure of outer hair cell functionand the expected measure of outer hair cell function.
 40. Thenon-transitory computer readable storage media of claim 38, wherein thewherein the instructions operable to generate, based on the comparisonresult, an acoustic prescription for the recipient comprise instructionsoperable to: determine, based on the comparison result, at least oneinput/output for at least a portion of the region of the cochlea. 41.The non-transitory computer readable storage media of claim 38, whereinthe wherein the instructions operable to generate, based on thecomparison result, an acoustic prescription for the recipient compriseinstructions operable to: determine, based on the comparison result, oneor more gain functions for the tonotopic region of the inner ear. 42.The non-transitory computer readable storage media of claim 41, whereinthe one or more processors are further configured to: obtain anaudiogram generated for the inner ear of the recipient; and determinethe one or more gain functions based on the comparison result and basedon the audiogram generated for the inner ear of the recipient.
 43. Amethod, comprising: delivering one or more sets of acoustic stimulationsignals to an inner ear of a recipient of a hearing prosthesis;obtaining, in response to the one or more sets of acoustic stimulationsignals, at least one measure of outer hair cell function from atonotopic region of the inner ear of the recipient; obtaining, inresponse to the one or more sets of acoustic stimulation signals, atleast one measure of auditory nerve function from the tonotopic regionof the inner ear of the recipient; comparing a value associated with theat least one measure of auditory nerve function to a value associatedwith the at least one measure of outer hair cell function to obtain acomparison value; and generating, based on the comparison value, anacoustic prescription for the recipient for frequencies below afrequency corresponding to the tonotopic region.